Carrier suppression modulator



Patented Sept. 6, 1932 UNITED STATES GEORGE n. UssE MAN, F ROCKY rom'r, NEWiORK, ASSIGNOR 'I'O RADIO eoaroRA- 'IION or AMERICA, A ooRroRATIoN or DEL W RE CARRIER "surrnnssron MODULATOR Application filed October 5, 1928. Serial No. 310,457.

This invention relates to carrier suspension modulation, and more particularly to a method and means for increasing the efiiciency of the usual type of carrier suppression modulator. V

The typical carrier suppression modulator consists of a pair of three electrode vacuum tubes with an input circuit so arranged that carrier energy is supplied to the control electrodes of the tubes in parallel, while modulating energy is supplied thereto in series. The output circuit being; connected between the anodes of the tubes, no carrier energy-is developed therein, but the modulating energy 1 and the side bands or'beat frequencies of the modulation appear in the output circuit. Because the input circuit is capacitive forfrequencies of the order of magnitude of the carrier and side band frequencies the feed back from the output circuit to the input circuit which takes place through the electrode capacitance of the tubes is degenerative in phase, and serves to diminish thedesired beat frequency output. It is an object of my invention to overcome this source 'of power loss, for which purpose I apply sufficient regeneration of the heat frequencies. to over comethe natural degeneration caused by, the interelectrode coupling.

VVhile the input circuit'is capacitive for high frequencies it is inductive for frequen-' cies of the order of magnitude of the'modulating energy, and therefore the effect of the feed back to the input circuits is regenerative, which is undesirable because the modulating frequency is an undesired frequencyin the output circuit anyway. Although this factor is reduced in importance by the tuning of the output circuit, it is not altogether negligible,

In accordance with my invention I apply sutficient degeneration of the energy of modulating frequency to overcome the natural regeneration thereof. V

A certain amountof energy is transferred to the output circuit from the input circuit directly through the-vacuum tubes as con-' densers, and not by reason of the usual vacuum tube action. This energy transferred is undesired, and is prevented by my invention. All of the foregoing steps I accomplish in a very simple manner byiproviding a pairv of condensers each connected between the anodes ofone of the tubes and the control densers, they provide regeneration for over-;

coming degeneration. At the same time the properties of the circuit are such that the desired and undesired frequencies are automatically discriminated between, so as not to provide regeneration of an undesired frequency, and actually to provide degeneration.

It is an object of my invention to still fur-. therincrease the eificiency of a carrier suppression modulator, and this I do by-overneutralizing the modulator, that is, by making the magnitude of the neutralizing condensers greater than whatis necessary for: correct neutralization, in which case the de sired energy is given a certain amountof positive regeneration, while the undesired'modulating energy is given a certain amount of positive degeneration; V .The inventi'n is described further inv the following specification, which is accompanied by a drawing,the single figure of which is e A a wiring diagram for one form of my invene tion.

Referring to the drawingthere is a pair of three electrode vacuum tubes 2, 4:, to the control electrodes-of which there is coupled an input circuit comprising an inductance 6 and the series'condensers 8 and 10 connected in parallel therewith. The modulating ener gy is supplied from any suitable source 12 to a coil 14 which is coupled to the input coil 6.

densers which freely pass thecarrier energy,

and are not intended to resonate with the inductance 6. A pair of chokes 18 and 20 may be provided to isolate the modulating and carri'erfre'quency paths. 5

The output circuit comprises an inductance 22, which, in the case of fairly constant frequency outputs, may be tuned by a tuning condenser 24. A speech side band may be tuned if impressed on a high frequency carrier. The condenser is preferably two series condensers, simultaneously tuned by a single control. The choke 23 prevents the tuned circuit from splitting up into two tuned circuits, in its action. The output circuit is connected between the anodes of the tubes 2, 4, as shown. The anodes are given a positive potential by a suitable direct current source connected to a lead 26, while the control electrodes are suitably biased by a source connected to the lead 28. I

In accordance with my invention a pair of condensers and 32 are connected, as shown, each from the anode of one of the tubes to the control electrode of the other of the tubes, and are adjusted to compensate, or to more than compensate for the effect of the natural capacitance between the output and input circuits of the modulator.

The blocking condensers 8 and 10 are, of course, capacitive for high frequencies, and it is a known property of vacuum tube circuits that the feed back to a capacitive input circuit is degenerative, which serves to diminish the magnitude of side band output. The condensers 30' and 32 serve to counteract this natural degeneration, and cause a desirable regeneration.

For low frequencies like the modulating frequency the input circuit is inductive, because the condensers 8 and 10 are a high reactance to this low frequency, and therefore the latter takes the inductive path 6. The natural coupling is in this case regenerative, but inasmuch asthe modulating frequency appearing in the output circuit is very undesirable, the regeneration is in this case also undesired. The condensers may be used to provide a degeneration which reduces the magni tude of whatever modulating energy may appear in the output circuit.

Another effect of great value is that the added condensers serve to prevent a transfer of energy from the input circuit to the output circuit directly through the capacitance of the tubes, instead of through the tubes by their proper tube action. This desirable result is best obtained without over neutralization.

WVith respect to the carrier energy the arrangement produces a certain amount of degeneration, but this is not especially injurious inasmuch as more current can be fed from source 16. This will not require more power, as the added current is reactive current.

What I claim is:

1. In carrier suppression modulation, the method of augmenting the output of energy of beat frequencies which includes providing sufficient regeneration of the beat frequencies to overcome natural degeneration.

2. In carrier suppression modulation, the method of augmenting the output of energy of beat frequencies .and diminishing the output of energy of input frequency which includes providing sufiicient regeneration of the beat frequencies to overcome natural de- 7 generation, and sufficient degeneration of an input frequency to overcome natural regeneration.

3. In carrier suppression modulation, the method of augmenting the output of energy of beat frequenciesand diminishing the outvide regeneration of the beat frequencies sufficient to overcome natural degenera'fion, and reactive means to provide degeneration of an input frequency sufficient to overcome natural regeneration. V

6. The combination with a carrier suppression modulator employing electron emission tubes of reactive means to over-neutralize the effect of the natural tube capacitance in order to provide positive regeneration of the beat frequencies, and reactive means to provide positive degeneration of an input frequency. I

7. The-combination with a carrier suppression modulator comprising a pair of electron emission tubes, a source of modulating energy coupled to the control electrodes of the tubes in series, a source of carrier energy connected to the control electrodes of the tubes in par allel through reactanccs which are capacitive at the carrier frequency, and an output circuit coupled to the anodes of the tubes, of a pair of condensers'each connected between the anode of one of the tubes and the control electrode of the other of the tubes for increasing the efficiency of the modulator.

8. An arrangement for carrier suppression modulation comprising a pair of electron emission tubes, and input circuit including an inductance and a pair of series connected condensers arranged in parallel with said inductance all connected in series with the control electrodes of the tubes, a source of modulating energy coupled to said inductance, a source of carrier energy coupled betweenthe condensers and to the cathodes of the tubes, an output circuit coupled to the anodes of the tubes, and a pair of condensers each connected between the anode of one of the tubes and the control electrode of the other of the tubes for increasing the efliciency of the modulator.

9. In a carrier suppression system, a pair of discharge devices having input and output electrodes; a source of carrier energy and a source of control energy coupled to the input electrodes of the devices, and means intercoupling the input and output electrodes of the devices to provide suflicient regenera tion of beat frequencies appearing in the output circuit of the devices, to overcome the natural degeneration of the devices.

10. In a carrier suppression system, a pair of discharge devices; a source of carrier energy coupled to the input electrodes of the devices and a source of modulating energy coupled to the input electrodes of the devices in phase and inphase opposition respectively; and means intercoupling the input and output electrodes of the devices to provide suflicient regeneration of beat frequencies appearing in the output circuit of the devices to overcome the natural degeneration of the devices.

11. In a carrier suppression system comprising a pair of coupled discharge devices having an input and an output circuit, the method of overcoming natural degeneration of beat frequency energy appearing in the output circuit of the modulator which includes applying carrier and modulating energy to the input circuit of the devices in phase, and in phase opposition respectively; and regeneratively feeding beat frequency energy from the output circuit of the devices to the input circuit thereof to overcome the natural degeneration of the devices.

GEORGE L. USSELMAN. 

